The intensity of sound wave while passing through an elastic medium falls down by 10% as it covers one metre distance through the medium. If the initial intensity of the sound wave was 100 decibels, its value after it has passed through 3 metre thickness of the medium will be [CPMT 1988]

• A.            70 decibel                              
• B.            72.9 decibel
• C.            81 decibel                              
• D.            60 decibel